This invention is in the field of digital circuits, and relates more particularly to low-voltage BiCMOS digital delay chains suitable for operation over a wide power supply range.
Many low-voltage digital circuits are required to operate over a relatively wide range of power supply potentials, such as from about 2.3 volts up to about 3.6 volts. Difficulties have been experienced in designing digital integrated circuits to fit these low-voltage applications, because integrated circuit performance varies substantially with power supply potential. In particular, because of the difficulty in creating simple zero-static-power, low-voltage digital circuits, corrective design techniques are required. One such technique employs monostable multivibrators or "one-shots" which remain "on" longer as the power supply potential becomes lower in order to compensate for the loss of speed at lower power supply potentials. There is a problem, however, in designing "one-shots" which create substantially longer pulses at lower power supply potentials while maintaining a relatively constant maximum repetition frequency.
Optimally, it would be desirable to create digital delay chains which provide high power supply potential sensitivity while switching in one direction but not the other, so that the maximum repetition frequency stays substantially constant with changes in power supply potential. Additionally, the digital delay chain should have a greater delay sensitivity 0to changes in power supply potential than to variations in fabrication process parameters.
Accordingly, it would be desirable to have a digital delay chain which is capable of providing a high sensitivity to power supply potential variations when switching in one direction but not the other, so that changes in integrated circuit performance with changes in power supply potential can be reduced. Additionally, it would be desirable to have a digital delay chain in which the sensitivity to power supply potential variations is substantially greater than the sensitivity to process parameter variations.